OBJECTIVES: 1. To measure the release of acetylcholine from longitudinal muscle-myenteric plexus strips of guinea pig small intestine in vitro under the influence of gastrin, octapeptide-cholecystokinin, vasoactive intestinal peptide, somatostatin, substance P, neurotensin and enkephalin, either singly or in combination. 2. To study the effects of these peptides, either singly or in combination, on cholinergic muscarinic receptor binding. 3H-quinuclidinyl benzilate will be used as a receptor probe. Both longitudinal and circular muscles will be studied. 3. To study the effects of ions/substrates on release of acetylcholine and binding of muscarinic receptor under the influence of these peptides. 4. To relate mechanical contracton in response to peptides to muscarinic receptor binding and/or release of acetylcholine in longitudinal muscle-myenteric plexus preparation.